Mining machine with laterally extensible trim chain sprockets and locking means therefor



1967 J. KARLOVSKY. JR 3, 7

MINING MACHINE WITH LATERALLY EXTENSIBLE TRIM CHAIN I SPROCKETS AND LOCKING MEANS THEREFOR Filed July 12, 1965 5 Sheets-Sheet 1 INVENTO yak/) KARLOVSK ,J/?,

A D A; Q

TTOEAZEY 3,350,137 HAIN J. KARLOVSKY JR Oct. 31, 1967 MINING MACHINE WITH LATERALLY EXTENSIBLIE TRIM c SPR'OCKETS AND LOCKING MEANS THEREFOR 5 Sheets-Sheet 2 Filed July 12, 1965 R Nu INVENTOR. JERRY K4RLOVSKKJR his @TTOEA/EJ Oct. 1967 J. KARLOVSKY, JR 3, 7

MINING MACHINE WITH LATERALLY EXTENSIBLE TRIM CHAIN SPROCKETS AND LOCKING MEANS THEREFOR Filed July 12, 1965 i 5 Sheets-Sheet 5 INVENTOR. JEAR r mqfizovs/(r, J2.

1967 .1. KARLOVSKY. JR

MINING MACHINE WITH LATERALLY EXTENSIBLE TRIM CHAIN SPROCKETS AND LOCKING MEANS THEREFOR Filed July 12, 1965 5 Sheets-Sheet 4 IN ENT JERRY KARL V BY J 4 his 3,350,137 HAIN 1967 J. KARLOVSKY. JR

MINING MACHINE WITH LATERALLY EXTENSIBLE TRIM C SPROCKETS AND LOCKING MEANS THEREFOR 5 Sheets-Sheet 5 Filed July 12, 1965 INVENTOR.

LOVSKY, J

)JJERRYKA 0 o 0 A 7- o e Vex United States Patent O 3,350,137 MINING MACHINE WITH LATERALLY EXTEN- SIBLE TRIM CHAIN SPROCKETS AND LOCK- ING MEANS THEREFOR Jerry Karlovsky, Jr., Nashville, Ill., assignor to National Mine Service Company, Pittsburgh, Pa., a corporation of West Virginia Filed July 12, 1965, Ser. No. 471,270 4 Claims. (Cl. 299-61) ABSTRACT OF THE DISCLOSURE A latch mechanism to positively lock a slidable cutter bar extension. A piston rod is connected to the laterally movable sprocket through a link member that also has functions as a latch mechanism. Outward movement of the piston rod extends the sprocket and pivots the link member to move the front edge portion of the latch arm downwardly into engagement with a fixed stop member. Inward movement of the piston rod pivots the link memher until it engages a second stop on the sprocket support and disengages the latch arm front edge portion from the fixed stop member. Further inward movement of the piston rod retracts the sprocket and engages a shoulder portion of the latch arm on the fixed stop member to limit further inward movement of the piston rod.

This invention relates to a boring type continuous mining machine having laterally extensible trim chain sprockets with locking means to maintain the sprockets in an extended position and more particularly to a boring type mining machine having hydraulically actuated laterally extensible trim chain sprockets with a mechanical locking means for maintaining the sprockets in an extended position.

The boring type continuous mining machine has a main frame with a plurality of shafts extending forwardly therefrom. The shafts have a plurality of radially adjustable cutting arms mounted on their front end portions that comprise forwardly extending rotary boring heads. Cutter bits are mounted on and extend forwardly from the cutting arms and are arranged to dislodge material upon rotation of the boring heads as the mining machine advances into the vertical face of material.

The continuous mining machine has upper and lower longitudinal slotted trimmer or cutter bars positioned rearwardly of the boring heads arranged to dislodge the cusps of material that remain between the bores formed by the boring heads. An endless trim chain is arranged to travel in the slotted portions of the upper and lower cutter bars and is suitably guided by a plurality of guide sprockets. The trim chain has cutter elements extending forwardly therefrom that remove the cusps of material and also enlarge the entry adjacent the bottom of the bore as will be later described. The endless trim chain is reeved about the guide sprockets and is driven by a drive sprocket suitably connected to the mining machine main transmission.

The cutter bars are adjustable vertically to accommodate the diameter of the bores formed by the radially adjustable cutting arms. To adjust the cutter bars it has been the conventional practice to pivot the lower trim chain idler sprockets adjacent the lower trimmer bar. US. Patent #2,991,059 discloses the pivotal arrangement of the lower sprockets.

In copending application Ser. No. 380,157, filed July 3, 1964, now Patent 3,278,237 entitled Mining Machine With Slidable Cutter Bar Extensions and assigned to the assignee of the present invention, there is disclosed apparatus for laterally extending and retracting the lower 3,350,137 Patented Oct. 31, 1967 idler sprockets along a horizontal line at the level of the lower cutting bar. The sprockets are hydraulically extended and retracted by means of a piston cylinder arrangement connected at one end to the mining machine and at the other end to a portion of the support for the trim chain sprocket. This arrangement for laterally adjusting the trim chain sprocket has markedly improved the operation of the boring type mining machine and has eliminated many of the previously present problems in trim chain and cutter bar maintenance and operation. The hereinafter described invention is an improvement on the apparatus described and claimed in copending application Ser. No. 380,157, now Patent 3,278,237.

The lower trim chain sprockets are extended to widen the bottom of the entry made by the mining machine and are retracted to facilitate withdrawal of the mining machine from the entry. Thus, during the mining operation When the mining machine is dislodging material from the vertical face, the lower trim chain sprockets are maintained in an extended position and are retracted only when the mining machine is being withdrawn from the bore. With the hydraulic actuating mechanism for the laterally extensible sprockets disclosed in copending application Ser. No. 380,157, now Patent 3,278,237, it was necessary, in order to maintain the trim chain sprockets in an extended position, to close a control valve and trap or retain hydraulic fluid within the cylinder and conduits. Because the extended position of the sprockets depends on a fixed volume of hydraulic fluid, even minute leakage in the system, as for example, around the piston or through the packing glands or seals, would result in the trim chain sprocket retracting. A means to positively lock the trim chain sprockets in an extended position would eliminate the problem of maintaining a fixed volume of hydraulic fluid in the hydraulic system while the sprockets are in an extended position and leaks in the hydraulic system would have no effect on maintaining the sprockets in an extended position. One of the problems encountered in positively or mechanically locking the trim chain sprockets in an extended position is the ability to remotely unlock the locking means when it is desired to retract the trim chain sprockets. As previously stated, it is necessary to retract the cutting arms, trimmer bars and trimmer chain sprockets when the machine is withdrawn from the entry. It is highly desirable for safety reasons to rapidly retract the extensible members so that the machine can be rapidly withdrawn from the mine face. In addition, the trim chain sprockets are not accessible to the operator and a manual locking means is, therefore, not feasible,

Briefly, the invention is directed to a mechanical locking means for automatically locking the lower trim chain sprockets in an extended position and automatically unlocking the mechanical locking means when hydraulic pressure is applied to retract the trim chain sprockets. The locking means includes a lock member that is hingedly secured to an end portion of the piston rod and also linked to the support housing for the trim chain sprocket. In an extended position the locking arm moves into abutting relation with a stop mechanism on the actuating cylinder to lock the trim chain sprocket in an extended position. When hydraulic pressure is applied to the cylinder to retract the trim chain sprocket, the lock member, through the link arrangement, is disengaged from the stop mechanism and moved into an unlocked position. The hydraulic pressure on the piston then retracts the trim chain sprocket.

Accordingly, the principal object of this invention is to provide a lock mechanism for an extensible trim chain sprocket that is unlocked when a retractive force is applied to the actuating mechanism for retracting the trim chain sprocket.

Another object of this invention is to provide a mechanical locking device for an extensible trim chain sprocket that engages when the trim chain sprocket is in an extended position and automatically disengages when hydraulic pressure is applied to retract the trim chain sprocket.

These and other objects and advantages of this invention will be more completely disclosed and described in the following specification, the accompanying drawings and the appended claims.

In the drawings:

FIGURE l is a view in front elevation of a boring type continuous mining machine with parts broken away to illustrate the trim chain arrangement.

FIGURE 2 is a top plan view of the trim chain sprocket lock mechanism in an extended locked position.

FIGURE 3 is a view similar to FIGURE 2 illustrating the trim chain sprocket in a retracted and unlocked position.

FIGURE 4 is a fragmentary view taken along the line 44 of FIGURE 3 illustrating the trim chain sprocket piston in an extended position and the lock mechanism in an engaged and locked position.

FIGURE 5 is a view similar to FIGURE 4 illustrating the manner in which the lock mechanism is disengaged from the stop mechanism when hydraulic pressure is applied to retract the trim chain sprocket.

FIGURE 6 is a view in elevation similar to FIGURES 4 and 5 illustrating in full lines the position of the lock mechanism when the piston is in a retracted osition and in phantom lines when the piston is in an extended position.

FIGURE 7 is a fragmentary perspective view of the mining machine illustrating the lock mechanism and the hydraulic mechanism for extending and retracting the trim chain sprocket.

Referring to the drawings and particularly FIGURES 1 and 7 there is illustrated a boring type mining machine generally designated by the numeral 10 that has a main frame 12 mounted on a pair of endless tracks 14 that serve to propel the mining machine. A gear case generally designated by the numeral 16 is supported by vertical cylinders 18 and pistons 20 suitably connected to main frame 12 (FIGURE 7). Iournaled in and extending forwardly from the gear case 16 are a pair of shafts 22 on which are mounted rotary boring heads 23 that have radially extensible cutting arms 24. The arms 24 have a plurality of cutter elements or bits extending forwardly therefrom that dislodge the material from the vertical face of material as the boring heads rotate. The boring heads 23 form a air of overlapping bores in the face of material being mined with cusp portions therebetween. A lower cutter or trimmer bar 26 is positioned transversely of the main frame 10 rearwardly of the boring heads 23 and arranged to remove the lower cusp remaining between the overlapping bores and the upper cutter or trimmer bar 28, similarly positioned relative to the main frame 12 and boring heads 23, is arranged to remove the upper cusp. The lower cutter bar 26 is adjustably mounted on the front end of the gear case 16 and is connected to a pair of adjusting cylinders 30 by means of rods 32 (FIGURE 7). With this arrangement the lower cutter bar 26 may be adjusted vertically by hydraulically moving the piston rods 32 within the cylinders 30.

The upper cutter bar 28 is supported by a pair of piston rods 34 that extend upwardly from cylinders 36. With this arrangement the upper cutter bar 28 may be similarly adjusted vertically relative to the gear case 16. The cutter bars 26 and 28 have horizontal grooved portions 38 therein which serve as a guide for trimmer chains. The cutter bar 26 also has a pair of extensible guide portions 40 that are connected to the journal housing 42 for the extensible trim chain sprockets 44. Thus, as the trim chain sprockets 44 are laterally extended, the lower cutter bar portions 40 are arranged to move laterally therewith.

The upper trimmer bar 28 has a pair of idler sprockets 46 and 48 rotatably secured thereto adjacent the end portions. The idler sprockets are arranged to guide the endless trim chain through the slots or grooves 38 in the upper cutter bar 28. A drive sprocket 50 is secured to the gear case 16 and is arranged to drive an endless trim chain designated by the numeral 52 and indicated in lines in FIGURE 1. Another idler sprocket 54 is supported by the gear case 16 and has the trim chain 52 reeved therearound. A take-up sprocket 56 is positioned adjacent to the drive sprocket 50 and maintains the desired tension on the trim chain 52.

The trim chain 52 is an endless link type chain, as illustrated in FIGURE 6 and has cutter elements extending forwardly therefrom. The trim chain is driven by drive sprocket 50 and is reeved about the lower idler sprocket 44 and guided through the grooves 38 in the lower cutter bar 26. The trim chain is also reeved about the extensible idler sprocket 44 on the opposite side of the lower cutter bar 26 and extends about idler sprocket 54 and is reeved about idler sprocket 48 connected to an end of the upper cutter bar 28. The trim chain is guided through the groove 38 in upper cutter bar 28 and around the other idler sprocket 46 to the drive sprocket 50. With this arrangement the endless trim chain 52 driven by drive sprocket 50 removes the upper and lower cusp members remaining in the face and provides a smooth, regular elliptical passageway in the face of the material being mined.

The lower cutter bar 26 has a pair of pusher plates 58 that extend upwardly therefrom and serve to guide the newly mined material into a central longitudinal throat 60 which has a conveying device therein to transport the newly mined material rearwardly on the mining machine away from the face. Additional pusher plates 62 may be provided to further assist in guiding the newly mined material toward the central throat portion 60. The pusher plates 62 are preferably connected to the journal housing 42 for the extensible sprockets 44. Thus, as the sprockets 44 are laterally extended the auxiliary pusher plates 62 are moved outwardly therewith. A floating pusher plate 64 is slidingly positioned in overlapping relation with auxiliary pusher plate 62 and is free to move radially outwardly in slots 66 to adjust to the width of the bore made by the boring head radial arms 24.

Referring to FIGURE 2, the trim chain sprockets 44 have a rearwardly extending shaft 68 that is journaled in a journal housing 70 and rotatably supported by tapered roller bearings 72 so that the idler sprocket 44 is supported by and freely rotatable relative to the journal housing 70. The journal housing 70 has a cylindrical shaft portion 74 extending laterally therefrom that is positioned in a cylindrical bore 76 of a support member 78. The support member 78 forms a part of the housing for the lower trimmer bar 26 and provides a suitable support for the laterally extensible idler sprockets 44. The cylindrical shaft portion 74 is axially movable within the cylindrical bore 76 to permit the idler sprockets 44 to be extended or retracted.

The journal housing 70 has a rear portion 80 with a laterally extending tongue like connector portion 82 adjacent the upper surface of the housing. The connector portion 82 has an aperture 84 therethrough. In FIGURES 4 and 5 the rearwardly extending portion 80 of journal housing 70 is illustrated in section and the tongue portion 82 is shown in full lines.

An adjusting cylinder 86 positioned below and to the rear of the journal housing shaft portion 74 has a clevis end portion 88 that is pivotally connected to the support member 78 by a pin 90. Within the cylinder 86 there is a piston (not shown) connected to a piston rod 92 that extends outwardly therefrom. The piston rod 92 has a tongue end portion 94 with a lateral bore 96 therethrough.

An L shaped latch mechanism generally designated by the numeral 98 has a vertical body portion 100 with an upper recess or slot 102. The body portions (FIGURE 3) on opposite sides of slot 102 have aligned apertures 104 and 106 extending therethrough. The journal housing tongue portion 82 extends into the slot 102 with the bore 84 aligned with apertures 104 and 106. A pin 108 connects the latch mechanism body portion 100 to the journal housing 80.

The lower portion of the locking mechanism body portion 100 has a similar recessed portion with aligned apertures therethrough in which the piston rod tongue end portion 94 is positioned with the bore 96 aligned with the apertures in the body portion 100. A pin 110 connects the piston rod end portion 94 to the latch mechanism body portion 100 at a location below the pin 108 that connects the journal housing 70 to the latch mechanism.

The latch mechanism 98 has an arm portion 112 extending laterally from the upper part of body portion 100 adjacent the pin 108. The arm 112 has a front edge portion 114 and a shoulder portion 116 on its lower surface. The cylinder 86 has a stop member 118 secured thereto by a weld 120, or the like.

The latch mechanism 98 is operable to lock the sprocket 44 in an extended position in the following manner. In a retracted position as illustrated in FIGURES 3 and 6, the latch member shoulder portion 116 abuts the front edge stop member 118 on the cylinder 86. As hydraulic pressure is applied to the cylinder 86 through suitable connections (not shown) the piston 92 begins to move outwardly from the cylinder 86 toward an extended position. The latch mechanism 98 through the double pin arrangement 108 and 110 tends to rotate in a counterclockwise direction as viewed in FIGURES 4, 5 and 6. The piston 92 in extending exerts a turning force on the lower portion of the latch mechanism body por- 'tion 100 and rotates the latch mechanism about the pin 108. Since the force is exerted on the lower portion of the latch body portion 100 the latch arm portion 112 slides on stop member 118 and after the latch arm end portion 114 moves beyond the end of the stop member 118 the latch mechanism rotates further in a counterclockwise direction to the position illustrated in FIGURE 4. In this extended position the latch mechanism 98 locks the sprocket 44 in an extended position. Inward or retracting forces exerted on the sprocket 44 are transmitted through the journal housing 70 to the latch mechanism and because the connection of the journal housing to the latch mechanism is above the connection to the piston 92 -the forces tend to rotate the latch mechanism 98 in a counterclockwise direction about pin 110 to thereby further urge the latch mechanism 98 into a locked position. In this locked position it is not necessary to maintain a fixed volume of hydraulic fluid within cylinder 86 to maintain the sprocket 44 in an extended position. The sprocket 44 remains in an extended and locked position until pressure is applied on the piston to retract the sprocket 44.

To unlock the latch mechanism 98 and retract the sprocket 44, hydraulic pressure is applied to the opposite side of the piston by suitable connections (not shown). The initial retracting movement of the piston rod 92 exerts a pulling force on the latch mechanism lower body portion at pin 110 and the latch mechanism 98 rotates in a clockwise direction about pin 108 and moves to the position illustrated in FIGURE 5. In this position the latch mechanism front end portion 114 is disengaged from the stop 118 on cylinder 86. Further retractive movement of piston 92 is transmitted through latch mechanism 98 toto the packing glands in the cylinder 86. A suitable abutment member 122 (FIGURES 2 and 3) may be provided on the journal housing rear portion to limit the rotation of latch member 98 about the upper pin 108.

Latch mechanisms 98 are illustrated as associated with both of the idler sprockets 44 on the mining machine 10. Where desired, one of the idler sprockets may be nonextensibly connected to the lower cutter bar 26 and only one of the sprockets 44 may be extended and retracted. Although the piston cylinder actuator for extending and retracting the sprocket 44 is illustrated as being positioned behind the journal housing 70, it should be understood that the piston could, with equal facility, be positioned above the journal housing, as is disclosed in copending application Ser.No. 380,157.

Although only one embodiment of this invention has been illustrated, it should be understood that the journal housing 70 and latch mechanism 98 could be fabricated with different configurations and accomplish the same purpose. For example, different types of connections could be made between the journal housing 70 and latch mechanism 98 such as a different clevis arrangement wherein the latch mechanism has a tongue portion that would extend into a recessed portion in the journal housing. Similarly, the end portion of the piston rod 92 could have a recessed portion and the latch mechanism lower body portion have an overlying connector portion.

It is believed one of the essential features of this invention is the link type of connection between the actuating piston and the journal housing with the latch mechanism 98 serving as the connecting link therebetween. The dimensions of the pins 108 and 110 and the bores in which the pins are positioned should be such that the latch mechanism 98 is free to rotate about pins 108 and 110.

According to the provisions of the patent statutes, I have explained the principle, preferred construction, and mode of operation of my invention and have illustrated and described what I now consider to represent its best embodiment. It should be understood, however, that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

I claim:

1. In a continuous mining machine having,

a trim chain sprocket,

.a journal housing to rotatably support said trim chain sprocket, said journal housing having a laterally extending support member,

a receiver on said mining machine for said support member,

said support member positioned in said receiver in a manner that said journal housing is-movable laterally relative to said mining machine,

a cylinder having a piston rod extending therefrom secured to said mining machine and extending laterally therefrom,

said piston rod connected tovsaid journal housing, and

fluid pressuremeans connected to said cylinder for extending and retracting said journal housing relative to said mining machine,

the improvement comprising,

a link member connecting said piston rod to said journal housing to permit limited relative movement between said piston rod and said journal housing, saifd link member having a latch arm extending thererom,

said latch arm arranged to lock said trim chain sprocket in an extended position and in a retracted position,

and said piston rod arranged upon movement toward said cylinder to rotate said latch arm and thereafter retract said trim chain sprocket to a retracted position where said latch arm engages abutment means to limit further retraction of said trim chain sprocket.

2. In a continuous mining machine having,

a trim chain sprocket,

a journal housing to rotatably support said trim chain sprocket, said journal housing having .a laterally extending support member,

a receiver on said mining machine for said support member,

said support member positioned in said receiver in a manner that said journal housing is movable laterally relative to said mining machine,

a cylinder having a piston rod extending therefrom secured to said mining machine and extending laterally therefrom,

said piston rod connected to said journal housing, and

fluid pressure means connected to said cylinder for extending and retracting said journal housing relative to said mining machine,

the improvement comprising,

a link member connecting said piston rod to said journal housing to permit limited relative movement between said piston rod and said journal housing,

said link member having a latch arm extending laterally therefrom adjacent one end,

an abutment means on said cylinder, and

said link member arranged upon outward movement of said piston rod to rotate in one direction relative to said journal housing and pivot said latch arm front edge portion into abutting relation with said abutment means and upon inward movement of said piston rod toward said cylinder to rotate in an opposite direction and pivot said latch member front edge portion out of engagement with said abutment means and engage an intermediate portion of said latch arm with said abutment means on said cylinder to limit further inward movement of said piston rod.

3. In a continuous mining machine having,

a trim chain sprocket,

a journal housing to rotatably support said trim chain sprocket, said journal housing having a laterally extending support member,

a receiver on said mining machine for said support member,

said support member positioned in said receiver in a manner that said journal housing is movable laterally relative to said mining machine,

a cylinder having a piston rod extending therefrom secured to said mining machine and extending laterally therefrom,

said piston rod connected to said journal housing, and

fluid pressure means connected to said cylinder for extending and retracting said journal housing relative to said mining machine,

the improvement comprising,

an L shaped latch member having a body portion and a horizontally extending arm portion, said arm portion terminating in an edge portion and having a stop mechanism positioned rearwardly of said edge portion,

said journal housing connected to said latch member body portion adjacent one end,

said piston rod connected to said latch member body portion adjacent the other end,

said latch member body portion forming a link member connecting said piston rod to said journal housing for extending and retracting said trim chain sprocket,

abutment means for said latch member,

said piston rod operable upon outward movement from said cylinder to extend said sprocket and move said latch member arm edge portion into engagement with said' abutment means to thereby lock said sprocket in an extended position, and

said piston rod operable upon inward movement toward said cylinder to move said latch member arm edge portion out of engagement with said abutment means and move said sprocket to a retracted position and engage said abutment means with said stop mechanism on said latch member to limit further retraction of said sprocket.

4. In a continuous mining machine having,

a trim chain sprocket,

a journal housing to rotatably support said trim chain sprocket, said journal housing having a laterally extending support member,

a receiver on said mining machine for said support member,

said support member positioned in said receiver in a manner that said journal housing is movable laterally relative to said mining machine,

.a cylinder having a piston rod extending therefrom secured to said mining machine and extending laterally therefrom,

said piston rod connected to said journal housing, and

fluid pressure means connected to said cylinder for extending and retracting said journal housing relative to said mining machine,

the improvement comprising,

an L shaped latch member having a body portion with an upper edge portion and a lower edge portion,

an arm member extending laterally from said body portion adjacent said upper edge portion, said arm member terminating in an edge portion and having a shoulder portion spaced from said edge portion,

said journal housing pivotally connected to said latch member body portion adjacent said upper edge portion said journal housing having an abutment member arranged to engage said latch member body portion,

said piston rod pivotally connected to said latch member body portion adjacent said lower edge portion,

said arm member extending toward said cylinder,

said latch member body portion forming a longitudinal member connecting said piston rod to said journal housing for extending and retracting said trim chain sprocket,

.a second member on said cylinder,

said piston rod operable upon outward movement from said cylinder to extend said sprocket and rotate said latch member about said connection to said journal housing and move said latch member arm edge portion downwardly into engagement with said second abutment member to thereby lock said sprocket in an extended position, and

said piston rod operable upon inward movement toward said cylinder to move said latch member arm edge portion out of engagement with said second abutment member and engage said latch member body portion with said journal housing abutment member to limit further movement of said latch member arm portion relative to said piston rod so that further inward movement of said piston rod retracts said sprocket to a position where said arm member shoulder portion engages said second abutment member.

References Cited UNITED STATES PATENTS ERNES B. FURSEB, Pri y Examiner- 

1. IN A COUNTNUOUS MINING MACHINE HAVING, A TRIM CHAIN SPROCKET, A JOURNAL HOUSING TO ROTATABLY SUPPORT SAID TRIM CHAIN SPROCKET, SAID JOURNAL HOUSING HAVING A LATERALLY EXTENDING SUPPORT MEMBER, A RECEIVER ON SAID MINING MACHINE FOR SAID SUPPORT MEMBER, SAID SUPPORT MEMBER POSITIONED IN SAID RECEIVER IN A MANNER THAT SAID JOURNAL HOUSING IS MOVABLE LATERALLY RELATIVE TO SAID MINING MACHINE A CYLINDER HAVING A PISTON ROD EXTENDING THEREFROM SECURED TO SAID MINING MACHINE AND EXTENDING LATERALLY THEREFROM, SAID PISTON ROD CONNECTED TO SAID JOURNAL HOUSING, AND FLUID PRESSURE MEANS CONNECTED TO SAID CYLINDER FOR EXTENDING AND RETRACTING SAID JOURNAL HOUSING RELATIVE TO SAID MINING MACHINE, THE IMPROVEMENT COMPRISING, A LINK MEMBER CONNECTING SAID PISTION ROD TO SAID JOURNAL HOUSING TO PERMIT LIMITED RELATIVE MOVEMENT BETWEEN SAID PISTON ROD AND SAID JOURNAL HOUSING, SAID LINK MEMBER HAVING A LATCH ARM EXTENDING THEREFROM, SAID LATCH ARM ARRANGED TO LOCK SAID TRIM CHAIN SPROCKET IN AN EXTENDED POSITION AND IN A RETRACTED POSITION, AND SAID PISTON ROD ARRANGED UPON MOVEMENT TOWARD SAID CYLINDER TO ROTATE SAID LATCH ARM AND THEREAFTER RETRACT SAID TRIM CHAIN SPROCKET TO A RETRACTED POSI TION WHERE SAID LATCH ARM ENGAGES ABUTMENT MEANS TO LIMIT FURTHER RETRACTION OF SAID TRIM CHAIN SPROCKET. 